+50 I'm assuming 3 1/2 is a mixed fraction.
If you get confused with mixed fractions, you can always convert them to normal fractions like \(\frac{1}{2}\).
\(3\frac{1}{2} \) converts to \(\frac{7}{2}\). You can find this by multiply the denominator(bottom of the fraction) by the integer part then adding the numerator(top of the fraction). You get \(3 \cdot 2 + 1 = 7\). Then divide that by the denominator or \(2\) to get \(\frac{7}{2}\). \(\frac{7}{2} \cdot 20 = 70\) because the \(2\) in the denominator cancels out with the \(2\) in the \(20\). Remember that \(20 = 2 \cdot 10\) which is why they cancel.
\(70\) is your answer.
